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SUMMARY It is shown that the washed muscle fibrils obtained from watery pork have a lower water retention at low ionic strength, and much lower extract‐ability at high ionic strength, than the fibrils from normal pork. These changes are accompanied by a gain of protein by the washed watery fibrils, and this protein originates from the soluble sarcoplasmic proteins. All the changes, including the characteristic gain of protein, can be artificially induced in normal meat by allowing it to pass into rigor at 37° C. The isoelectric region, or region of minimum swelling of watery fibrils, whether washed or unwashed, is similar to or slightly lower than that of normal fibrils. There is a broad isoelectric zone in both cases, extending from ∼pH 5 to ∼5.70. On the other hand, the IP of fully coagulated fibrils lies between 5.6 and 6.1. Washed and unwashed fibrils of watery meat show about the same degree of swelling at all pH values. Normal fibrils, however, show a higher water retention in the unwashed state than the washed. This effect is not due to the Mg or Ca ions included in the unwashed samples, but may result from interaction between the sarcoplasmic and fibrillar proteins. In the unwashed state, the swelling of normal fibrils is nearly double that of the watery fibrils at all pH values. It is shown that the rise of pH in intact carcasses of watery meat as they cooled from 37 to 10° C was probably due to the effect of temperature on the pK of ionizable groups of the proteins and buffering substances. It can be reproduced artificially and reversibly in native and coagulated minced meat, merely by raising or lowering the temperature. The titration curves of watery fibrils show similar titration constants (pK') to those of normal fibrils, but a loss of ratable groups. Heat coagulation, on the other hand, results not only in a bigger loss of titratable groups but in a much larger shift in the titration constants. These results can be interpreted to show that the fibrillar proteins of the watery fibrils are not denatured or aggregated in the usual sense, but are probably covered by a layer of denatured sarcoplasmic protein that is firmly‐bound to the surface of the myofilaments.

In a recent paper (Bate-Smith & Bendall, 1949) it was shown that the timecourse of rigor mortis in rabbit muscle was determined principally by the glycogen-reserve of the muscle at death. As it had previously been shown (Bate-Smith & Bendall, 1947) that the 20-to 40-fold increase in the modulus of elasticity of the muscle, characteristic of the rapid phase of rigor, coincided with the rapid disappearance of adenosine triphosphate (ATP) from the muscle, the conclusion was drawn that the glycogen was merely acting as a reserve of energy for the resynthesis of ATP. In neither of these papers, however, was the role of creatine phosphate (CP), as a reserve of energyrich phosphate, fully taken into account, nor was direct evidence offered that it did not disappear from the muscle coincidentally with the ATP. In the present paper it will be shown that in well-rested and relaxed animals, the CP level is high immediately postmortem, but decreases rapidly thereafter, being reduced to less than 30 % of its initial level before there is any appreciable loss of ATP. This occurs whatever the rate of glycolysis, although the rate of breakdown of CP depends to some extent on the glycogen reserve at death.For well-fed, rested animals, the chief chemical events related to the onset of rigor mortis are (a) more or less rapid glycolysis from the moment of death, the rate depending on the pH-range traversed (cf. Bate-Smith & Bendall, 1949), (b) the disappearance of CP from the moment of death, the CP falling to 30 % of the resting level when the pH has fallen to about 6-8, (c) the disappearance of ATP, which begins when the CP has fallen below the 30 % level, and continues at a steady rate until it reaches 20 % of its resting level. At this point glycolysis is almost at a standstill, and the rate of ATP disappearance falls off markedly. As in the previous paper, the rate-determining factor in all these reactions is taken to be the breakdown of ATP by the ATP-ADP-ase systems in muscle,